U.S. Pat. No. 4,707,056 discloses spectrometers and demultiplexers having mechanically divided or holographic concave gratings. The entrance slit and exit plane lie substantially on the Rowland circle. In a compact and robust embodiment, the optical components are mounted on a glass or plastic body. It is known to arrange a diode array in the exit plane in spectrometers of this kind.
However, a considerable danger of breakage exists with the required cementing of the diode array to the spectrometer. Furthermore, commercially available diode arrays are built into housings and for this reason cannot be mounted directly on the spectrometer body.
A planar Rowland spectrometer is disclosed in the paper of H. W. Yen et al entitled "Planar Rowland Spectrometer for Fiber-Optic Wavelength Demultiplexing" published in the journal "Optics Letters", Vol. 6, no. 12, December 1981, pages 639 to 641. This planar Rowland spectrometer has a base body in the form of a slab waveguide on which a cylindrical concave grating is mounted. The slab waveguide has an end face facing away from the grating which has the contour of the Rowland circle. Radially arranged light-conducting fibers operate as signal outputs.